Not all things blend well
Oil and water, a classic analogy for anything that doesn't combine well or at all. Like personalities and substances. With materials (and with people), combining certain substances (personalities) can form a volatile mix. Most people know not to blend house hold bleach and ammonia because they produce a toxic gas. Mixing vinegar and baking soda also creates a volatile reaction, however its simply fun to watch.
With buildings and houses, the same caution and knowledge needs to be applied. Mixing the wrong materials can cause detrimental reactions. A common example found in houses would be galvanic corrosion. Two dissimilar metals will react, depending on the amount of moisture, causing deterioration to the less noble material. The most recent example of this would be the newer formulated pressure treated woods and the flashings used with them. In particular aluminum. Since the newer woods are treated with more copper, the wood or actually the copper in the wood reacts with the aluminum, causing deterioration.
While inspecting the foundation of a newer house (1986), I discovered an unusual amount of cracking in the foundation walls. Now some degree of cracking in foundation walls is fairly frequent and not unexpected. What made this cracking unique was that it was pervasive throughout the visible portions of the walls. Also strange was the way in which the walls were cracking. Most common are single cracks running vertical / diagonal. These were spider web cracks. The larger cracks were running horizontal. The portions of the foundation walls below grade were covered in efflorescence, indicating that the cracks were transporting moisture and possibly water at times. Due to these conditions, my recommendation was to have an engineer further examine the walls.
Some days later I heard from the buyer's agent. The clients had walked away from the house and would be needing another inspection. He proceed to tell me about the foundation.
An engineer was hired to examine the walls as advised. His conclusion was the condition of the foundation was likely due to an alkali–silica reaction. To confirm the condition would require taking a core sample of the wall and expensive testing. He also found that the rear foundation wall was bowing inwards. The foundation over all was defective and failing.
The agent went on to say that after some research, the foundation issue was known to be present in other houses in the area and due to one particular company using an incompatible aggregate in the concrete mix. The reaction is said to take many years to manifest, about 15 - 20.
It is the concrete company's responsibility to test the aggregates they use and adjust the mix accordingly to prevent a reaction. The foundation condition is due to negligence on the concrete companies part. The repair is a new foundation must be poured. An estimated cost of $50,000.
While the buyer was saved from a huge future expense, the present owner is stuck with a house that is either un-saleable or must be sold at a significantly reduced price.
I think that they probably had a bad reaction to the news.